1. Field of the Invention
The present invention relates to a computer-readable storage medium having stored therein an image processing program for displaying an image of a virtual object such that the image of the virtual object is superimposed on a real space that is visible by a user, and relates to an image processing apparatus, an image processing system, and an image processing method.
2. Description of the Background Art
There is a conventional apparatus for superimposing a virtual object on an image of a real space that is captured by a real camera, thereby generating an image in which the virtual object looks as if the virtual object actually existed in the real space, and displaying the generated image on a display device. For example, an apparatus disclosed in Japanese Laid-Open Patent Publication No. 2003-256876 (hereinafter, referred to as Patent Document 1) captures, with a real camera, an image of an object indicator which is placed in a real space, and calculates the position and orientation of the object indicator in the real space. Then, a three-dimensional model is placed in a virtual space such that the position and orientation of the three-dimensional model in the virtual space correspond to the calculated position and the orientation in the real space. A virtual camera captures an image of the three-dimensional model placed in this manner in the virtual space. The image captured by the virtual camera is superimposed on the image captured by the real camera, and the resultant image is displayed.
However, according to Patent Document 1, the manner of displaying the virtual object is the same regardless of the environment of the real space, the image of which is captured. Therefore, a situation may arise where the displayed virtual object looks unnatural. For example, if the real space is dark, the entire image captured by the real camera also becomes dark. However, since the brightness of the virtual object superimposed on the image captured by the real camera does not change, only the virtual object is displayed in a manner to look bright. As a result, the virtual object unnaturally stands out in the display.